Piezomechanik GmbH
Position
Feedback control electronics

PosiCon.anfor piezoactuators(low voltage and high voltage actuators)

Above:
PosiCon 150/3 with actuator PSt 150/14/20 VS 20, option: position detection.
Sensor: white cable and actuator: brown cable are connected to channel I.

株式会社キーストンインターナショナル
277‑0042 千葉県柏市逆井 13‑27 黒沢ビル 3F
TEL: 04-7175-8810 key@keystone-intl.co.jp

Precision positioning by piezoactuators:
open and closed loop operation
One essential feature of a piezoceramic actuator is its
ability to make infinitely small movements, when a correspondingly small voltage signal is applied.This enable piezoactuators for ultraprecise positioning tasks (unlimited relativepositioning sensitivity).

On the other hand, when a large change in the voltage signal
is applied to a piezoactuator, the actual position stepwidth
can be influenced by a lot of internal and external parametersacting onto the actuator, so that in the first instant, the relationship between voltage and the induced motion can only
roughly be predicted. This can be easily demonstrated byapplying a series of random voltage steps to a piezoactuator(Fig. 1) or by running a cycle over a distinct voltage range
producing the wellknown hysteresis loop.

Hysteresis

→

1.0
0.9→

0.7→

displacement (normalized)

0.8

0.6
0.5
0.4
0.3
0.2
0.1
0.0→ input voltage

-0.1
-1

0.0

1

2

3

45V

Fig.1
Open loop correlation of piezo actuator’s position and driving voltage for a sequence of random voltage steps.
Additionally the usual hysteresis cycle for a continuous full scale voltage variation is shown.
The randomly generated sequence of points is filling up the area envelopped by the hysteresis cycle.

When a distinct piezo voltage level is accessed from randomly distributed starting points of the actuator, the incertainty in the final position is roughly equivalent the intersectof the hysteresis field with the voltage level.
So the incertainty in open loop piezo positioning in random
access operation can be up to 10 % to 15 % of the actuallyapplied total piezo actuator range.

(In fig.1 the characteristic of a low voltage actuator PSt 150 isshown equivalent a full output voltage range –30 V thru
+150 V. The hysteresis intersect (position incertainty) for
2.5 V input signal at open loop operation is indicated.

How can this seemingly contradiction to “ultraprecise positioning” be overcome:By feedback controlled closed loop positioning:
The PosiCon System3Basics of closed loop operation:
The actuator produces only a motion, but does obviously notcontain inherently a precise information about the exact position.
To get this information about the actual position, the actuator
must be combined with a suitable kind of position sensitiveeffect or sensor. “Suitable” means: sufficiently high in accuracy, repeatability, linearity.
By a feedback control logic, the real position of the actuatoris permanently compared with the wanted position, definedby the magnitude of the input signal. When there is a difference between wanted (reference) and real position, the feedback control cancels it immediately out (closed actuatorsensor loop operation) and the systems settles at the perfect position.
Fig. 2
Relation stroke – reference input voltage to a piezomechanical systeminA open loop operation (by standard amplifier or PosiCon in “feedbackoff” mode)
Result: typical piezoactuator nonlinear hysteresis characteristic.
Hysteresis about 15 %B closed loop operation of a PosiCon system together with an actuatorwith position sensor
Result: linear characteristic with a residual hysteresis: order of magnitude 0.1 % of actuators maximum stroke

What are the advantages of the feedback controlled PosiCon system
Piezoactuators stroke is measured by a position sensor(strain gage) applied directly onto the piezostack inside
the casing:Hereby the sensor detects all internal and external
effects influencing the strain status of the stack:The result is a

• highly linear and reproducible motion of the actuatoraccording the input reference signal (elimination ofpiezomaterials creep, hysteresis, nonlinearity).
• automatic selfcompensation for varying load forces,
potentially changing the strain of a piezo stack: thePosiCon system shows virtually infinite stiffness(no change of strain under varying forces).
• Special thermally compensated strain gages are usedwhich compensate even for a potential thermal expansion of the actuator.
Fig. 3: Variety of piezoactuating components with surface mounted
strain gauges

4The PosiCon Philosophy

The “PosiCon.an” piezo positioning system is a complete
system comprising all necessary electronic subsystems for
closed loop piezo actuator control (Fig. 4):• position sensor signal amplifier stage• feedback control logic• piezo voltage amplifier (SVR type standard)“Plug and play”:
Connect your piezo actuator and its position sensor to thePosiCon.an unit and put in your position control signal:that’s allFig. 4
Modul Structure of the PosiCon feedback control unit

Technical details:
General:For feedback/closed loop operation, the piezo actuator
must accept the voltage range of the PosiCon.an device
and show option “position sensor”(see actuator’s data sheet)
The PosiCon.an feeback controllers use analog feedback
strategy.
The standard versions use SVR high voltage output stages
to supply the piezo actuators (see general catalog “electronicsupplies”)
A wide range of positioning applications using even mid-sizedactuators are covered with respect to precision and responsetime.
The SVR amplifier stages provide semi-bipolar operation
for largest stroke and feature lowest noise for highly stable
positions together with a smooth reaction characteristic of
the positioning system.

Fig. 5:Functional block diagram of a PosiCon system

Dual use:

Response time

The PosiCon.an devices can be used in “closed loop” or“open loop” mode.
The mode selection is done simply by a switch on the front
panel.
For multichannel devices, each channel can be set individually.
In the “open loop” mode the PosiCon.an acts as simple
piezo amplifier as described in catalog “Electronic supplies
for Piezomechanics”.
Position information is provided even in the “open loop”
mode (see “Display” and “Monitor”)

The closed loop response time of a feedback system isdefined as the settling time when a new position is addressed.
With a well adjusted control loop and sufficient high output
power, the settling time can be shorter than 10 msec.
The response time depends to some extent on the capacitance of the actuator and can further be affected by external
influences too e.g. by changing the mass load of an actuator
orRepeatability, Sensitivity
Precision means the tolerance range for hitting a wanted
position upon application of the equivalent input signal.
A, for random access addressing of a position, the PosiConsystem can show a repetition tolerance of about +/– 1“.
A 50 mm actuator can be operated within a +/– 50 nanometer tolerance field (residual hysteresis)
B, the repeatability is still better for cyclic motion profiles
C, the minimum resolvable relative shift in position is about
5 nm in the closed loop mode.

Stroke, forces and stiffness
A closed loop systems shows virtually infinitely high stiffness:a change of force load does not change actuator’s position.
On the other hand: As shown in the brochure “Piezomechanics: An Introduction” chapter 1.3 piezo actuators show fullstroke only, when there is no or neglectable change of theaxial force balance acting on the piezo actuator. When axial
forces are varying during piezo actuator’s action, then thestroke is reduced.
The fundamental limit of PosiCon.an is reached when theblocking force is applied:In the closed loop mode the PosiCon.an is encountering forthe potential compression by applying the maximum voltage.
No further change of stroke is possible.

5Functional elements (see front-page)“Offset”
PosiCon.an unit show an “offset” potentiometer per channel
for manual setting of a DC-input signal level.
According the “dual use” philosophy of the PosiCon.an
system, the function of “Offset” is twofold:
Closed loop operation:
A manual setting of the position can be done.
The position varies linearely with “Offset”, no hysteresis andcreep.
Variations in position by varying load forces are compensated for automatically.
The “offset” setting is superimposed to external signals,applied to PosiCon.an’s inputs.
Open loop operation
A manual setting of the output piezo voltage can be done.
The position of the actuator varies with “Offset” resulting in
the normal open loop behaviour with hysteresis and creep.
The “offset” setting is superimposed to external signals.

Piezovoltage output:
The connecting system is
BNC for 150 V / 500 V devices
LEMO 0S.250 or 1000 V devices
Optionally, other connecting systems like LEMO 00 250 areavailable.

LC-displays
for individual “mm” and “Volt” reading per channel

Optional High Power PosiCons:To drive large piezo actuators with high dynamics thepower requirements may exceed the range of the standard
PosiCons.

Each channel of the PosiCon.an is provided with a double
LCD read out both for stroke and piezo voltage.
Even when the system is running open loop, you get information about position.
Zero-setting:
The starting point of piezo actuator’s action can depend on
various side conditions like mounting forces, preloading etc.
To get a reasonable position read-out, each channel for thePosiCon can be set to “zero” individually by a potentiometerin the front panel.
Gain factor:
The amplifier gain factor of each channel of the PosiCon
can be set individually by a switch to accept alternatively
5 V or 10 V input signal for full stroke action.
“Open/closed loop” selector switch “Feedback”
Each channel of the PosiCon can be selected by a switch for“open loop” or “closed loop” operation.
In the “open loop” mode, the PosiCon behaves like a normal
piezo amplifier.
Position detection remains active, so position information
is provided via “LC-Display” and “Monitor”.
“Monitor”
Via BNC connectors on front and rear panel, analog signals
are provided as real time information for position and piezovoltage for each channel individually.
Piezovoltage is reduced by a factor 1:1000.
Position is represented as a 5 V swing equivalent full stroke.
Sensor input:
The PosiCon.an unit requires a signal from a 4-element
Wheatstone bridge for input.
This sensing element is usually applied to the piezo actuator(Option: position detection).
But the sensor can be attached to an external mechanism
too, where the piezo actuator’s motion leads to an equivalent
deformation (e.g. hinges of flex stages).
The electrical connecting system is 4-pole LEMO 0S.304

6Output voltage ranges for standard PosiCon.an devices.
The standard PosiCon.an incorporates SVR amplifier stages
as described in catalog “Electronic supplies”. The uniquefeature is the semibipolar voltage range resulting in a 20 % to30 % increase of piezo actuator stroke compared to unipolar
devices.
PosiCon.an 150: – 30 V thru +150 V / max. current: 60 mA
PosiCon.an 500: – 100 V thru +500 V / max. current: 15 mA
PosiCon.an 1000: – 200 V thru +1000 V / max. current: 8 mA

Optionally High Power PosiCons can be offered on the baseof high power amplifier stages
LE150/025
LE430/015
LE150/100
LE150/200
LE1000Calibration:
Calibration is only necessary to set the position read outsof the PosiCon.an (“mm”-LCD and “Monitor”) to the actuator
performance.
Calibration is done at PIEZOMECHANIK factory and is valid
for the distinct actuator-PosiCon combination.
Uncalibrated systems work in “closed loop” feedback
mode too (compensation for hysteresis, creep etc.), only theposition read outs are not valid.
Available configurations, ordering information
The standard PosiCon.an systems are offered in single andtriple channel arrangements.
e.g. PosiCon.an 150/1 or PosiCon.an 150/3.
High power PosiCons are usually delivered as single channeldevices.
On request other configurations are offered.

Piezomechanik’s product rangePiezo stack and ring actuators:

low voltage and high voltage types

high dynamic elements for adaptive structure control

rapid valve switchingcryo applications down to the sub-Kelvin levelvery long stroke high load elements

high temperature applications (up to 200 °C)



UHV application

Space applications

Special designed elements

Bipolar actuators

Analog / switching amplifiers Voltage controller type+150 / +200 V: up to 50 Amperes peak+500 V: up to 20 Amperes peak+1000 V: up to 15 Amperes peaksemibipolar supplies for widest range piezo-deflection
 Current and charge controlling amplifiers:
for open loop linear and hysteresis free high dynamic operationof piezo actuators
low and high voltage / low and high power versions available
 High power, electronic pulsers:
pulse powers up to 500 KiloWatts
low and high voltage versions
 Constant current pulsers for charge control piezo-driving strategy
e.g. in highest speed / high power valve and fuel injection control

7

株式会社キーストンインターナショナル

Piezomechanik · Dr. Lutz Pickelmann GmbH
Berg-am-Laim-Str. 64 · D-81673 Munich · Phone ++ 49/ 89 / 4 3155 83 · Fax ++ 49/89/4 31 6412
e-mail: info@piezomechanik.com · http://www.piezomechanik.com

Stand: Januar 2004

277‑0042 千葉県柏市逆井 13‑27 黒沢ビル 3F
TEL: 04-7175-8810 key@keystone-intl.co.jp